Indirect heat exchange

Kwasniak [312] investigated the heat transfer behavior in the water/parafifin dispersion with = 5-95% oil in water and established, that none of the evaluation relationships for the S/L systems [neither according to expression (7.40) nor according to expression (7.44)] produced a satisfactory correlation. Thereby fee was calculated according to expression (7.38), but fi was calculated according to expression (6.24) (e - emulsion). 

The higher the volume fraction of the oil was, the more strongly the experimental data deviated from the particular relationship downwards. Only if the paraffin oil forms the continuous phase (phase inversion at 70% oil), can the heat transfer be well described by the relationship according to expression (7.44). 

From this it was concluded, that the boundary layer is also not free of oil droplets for small volume fractions of the organic phase and that these partially occupy and insulate the wall. If the organic phase forms the continuous phase, the boundary layer consists of two layers, whereby that closest to the wall consisted of a pure oil phase and the outer of the oil/water-dispersion. 

By addition of a surfactant, the wetting of the wall by oil droplets is avoided and the heat transfer characteristic can be well described by the equation (7.44) incorporating the values fe, h and for water, see Fig. 7.11. 

Heat transfer in the gas/liquid/solid [G/L/S) material system can be represented in the same framework as that in the G/L material system, see expression (7.36), if the material values of the L/S systems were averaged. It emerged, that the St values in suspensions were slightly lower than in the G/L system alone [523]. 

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Vacuum Treatment. Milk can be exposed to a vacuum to remove low boiling substances, eg, onions, garlic, and some silage, which may impart off-flavors to the milk, particularly the fat portion. A three-stage vacuum unit, known as a vacreator, produces pressures of 17, 51—68, and 88—95 kPa (127, 381—508, and 660—711 mm Hg). A continuous vacuum unit in the HTST system may consist of one or two chambers and be heated by Hve steam, with an equivalent release of water by evaporation, or flash steam to carry off the volatiles. If Hve steam is used, it must be cuUnary steam which is produced by heating potable water with an indirect heat exchanger. Dry saturated steam is desired for food processing operations. 

The feed to a distillation tower is normally heated either by indirect heat exchange with hot products and/or in a furnace. The products must be condensed and cooled. This is accomplished in part by heat exchange with other petroleum streams and in part by cooling water exchange. The arrangement and relative... 

There are two types of snow cooling system. One is direct heat exchanging system and the other is indirect heat exchanging system. Direct heat exchanging system is the same as the forced convection type. Room air is circulated between a room and a stored snow room by fans and cooled directly. The advantages of this system are... 

From these reasons, almost large snow cooling systems adopted indirect heat exchanging system. In indirect system, a water-water-type heat exchanger is used between primary and secondary system. Figure 186 shows an application of direct heat exchange system. 

Unlike the methane steam reformer, the autothermal reformer requires no external heat source and no indirect heat exchangers. This makes autothermal reformers simpler and more compact than steam reformers, resulting in lower capital cost. In an autothermal reformer, the heat generated by the POX reaction is fully utilized to drive the SR reaction. Thus, autothermal reformers typically offer higher system efficiency than POX systems, where excess heat is not easily recovered. 

Reactions with a large heat of reaction as well as reactions that are very temperature-sensitive are carried out in reactors in which indirect heat exchange occurs with a heat transfer medium which is circulated through the fixed bed. 

Deodorization. This process should be a minor contributor however, it can produce significant waste loads if the deodorizer does not have a well-operated scrub cooler. The barometric recycle should have its oil separator/skimmer. In certain instances, an indirect heat exchange system is employed to reduce odor problems... 

Heater This may be an indirect heat exchanger or a direct-fired burner, or heating may be electrical (including RF/microwave absorption). 

FIGURE 10.1 Flowsheet for the electric furnace process for the production of elemental phosphorus. Phossy water from the phosphorus phase separator (sump) is normally maintained in a closed-circuit holding pond system which also provides the feedwater for the phosphorus direct contact condenser. Some facilities have a further indirect, heat exchange condenser for the carbon monoxide stream, after the direct contact condenser. 

Ammonia conversion takes place at 400-500°C. Most of the input gas heating is provided by indirect heat exchange with already converted exit gases via an exchanger inside the pressure shell of the converter (Fig. 11.3). During the fraction of a second contact time, the feed gas stream forms a gas... 

Gas exposure times to furnace temperatures are kept short by a direct spray of ethylene dichloride at ambient temperatures onto the exit gases and by an indirect heat exchanger. Hydrogen chloride may be recovered by scrubbing with water, or by some form of fractionation if it is to be fed in anhydrous form to an oxychlorination unit. Many vinyl chloride producers operate an oxychlorination unit solely to convert the by-product hydrogen chloride from the ethylene dichloride cracker to produce additional ethylene dichloride feedstock. Vinyl chloride (b.p. —13.4°C) is almost entirely consumed for the production of poly(vinyl chloride) (PVC). 

The basis of the LT technology is the thermal processor, which is an indirect heat exchanger used to dry and heat contaminated soils. Heating the soils to approximately 500 F in the processor evaporates or strips the organics from the soil. The organic vapors are then vented through two condensers which operate... 

In view of these temperature rises, a fixed-bed reactor would be feasible only if the oxygen could be added in stages in a multi-bed reactor so that the temperature rise across each bed were limited. Interstage cooling could be accomplished by injection of recycle methane and indirect heat exchange. For example, if the performance in each reactor bea is as shown in Fig. 2a, the temperature rise across each bed will be 46°C. Laboratory experiments [ref.4] have shown that selectivity is not significantly affected by a temperature rise of this magnitude. 

The two electrolytes are cooled by indirect heat exchange outside the electrolyser, in which they flow rapidly, to avoid a temperature rise of more than 3°C, and to limit the concentration of adiponitrile at the cathode surface. The cells, grouped in batteries of twelve, have a capacity of3020 kW each. They are supplied with 440 V power, at 33 A/dm2. Each ceil can produce 70 kg of adipaoitrile per hour. 

This preheating can be achieved by indirect heat exchange between hot product gases. This is practised in the manufacture of cement clinker. The clinker is cooled in process air, which is thus preheated for the precalcination step. The next calculation example treats a simplified case of this type. 

To reduce the space required for this recovery, to improve the density and control the purity, and to reduce the amount of manual labor required, it has been proposed to accomplish recovery by use of a sequence of steps (1) cool the vaporous mixture by passage through a water-cooled tubular cooler condenser, (2) remove the bulk of the condensed material by means of a scraper-screw conveyer in the cold end of this cooler, and (3) recover dust from the cold gases by means of a bag filter. Fractional condensation of phthalic anhydride from gas-vapor mixtures containing maleic anhydride may be accomplished by maintaining the mixture in the temperature range of 80-90 C to 132 C by indirect heat exchange with a fluid confined in tubular conduits. ... 

While alkylation reactore can employ indirect heat exchange, the one depicted in Fig. 14-5 and dettuled in Fig. 14-6 employs autorefrigeration by... 

Fig. 2.3.1-8 Examples of indirect heat exchenge. a) Direct cooling with recirculating quench, b) Combination of direct and indirect heat exchange.

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